Dr. Yu-Jung Lee is a board certified pathologist who earned his M.D. and Ph.D. degree in immunology at Seoul National University, Collage of Medicine. His Ph.D. thesis research was on innate T cell development by homotypic thymocyte interactions, where he found a key role for the transcription factor PLZF, and that IL-4 produced from PLZFhigh T cells conditioned CD8 T cells to become memory-like. After his dissertation work, he joined Dr. Hogquist's lab and focused on the thymic development of iNKT cells, showing that iNKT cells differentiate into 3 major subsets, and that IL-4 produced by one of these subsets has broad effects on immunity. In this proposal, he seeks to become a tenure track scientist in a world-class research institute to pursue an independent career as an immunologist. To achieve this goal, he has planned further research on iNKT cell subset differentiation and their potential roles in autoimmune disease. iNKT cells have long been considered an immunotherapeutic source of IL-4 to suppress Th1 or Th17 mediated autoimmune disorders. However, clinical trials in humans were not successful as these cells failed to produce abundant IL-4 as seen in mouse model systems, suggesting that our previous understanding was incomplete. Dr. Lee's research recently provided evidence that revised the iNKT cell developmental paradigm, showing that transcription factors such as T-bet, GATA-3 and ROR?t regulate the lineage differentiation program of a PLZFhigh common progenitor into NKT1, NKT2 and NKT17 cells, respectively. Precursor/progeny analysis revealed these subsets are terminally differentiated mature cells and each subset had a distinct priority for cytokine secretion according to their transcription factor expression; NKT1 cells for IFN-?, NKT2 cells for IL-4, and NKT17 cells for IL-17. NKT2 cells, especially, were the primary source of IL-4 at steady state and upon activation with synthetic glycolipids. Based on these findings, we reasoned that NKT2 cells can prevent Th1 or Th17 mediated autoimmune disorders, whereas NKT1 or NKT17 cells would worsen them. This research will identify factors regulating lineage the differentiation program of iNKT cells in vivo. We hypothesize that cytokines regulate the lineage differentiation of iNKT cells, and dendritic cells provide stimulatory ligands for NKT2 cells, causing them to secret IL-4 at steady state. Furthermore, an in vitro lineage differentiatio protocol for iNKT cells using the OP9-DL1 culture system will be developed. We will test the therapeutic efficacy of these cells in in vivo mouse models of autoimmune disorders. The results obtained in this study will provide important implications for NKT-based immunotherapy of human disease.